Knapster is an open source, independent implementation of the Napster protocol client. It
is written to conform to the KDE windowing environment.

Problem: It is possible for anyone to obtain any user-readable file by sending a
properly formed "GET" command that contains the full path of
the file. This vulnerability exists because knapster
fails to check that the requested file is an explicitly shared MP3 file
before providing it.
Note: This is the same vulnerability described in FreeBSD-SA-00:18 but in
knapster instead of gnapster.
Anyone running knapster version 0.9 or less is vulnerable. Given the
IP address and TCP port of a vulnerable client, an attacker can
send a request for an arbitrary file to the knapster client. If the
user has read access to the file, the client will then respond with
the contents of the file.

Solution: We contacted the program's author, and he promptly created
a new version which addresses this vulnerability. The fix simply
checks that a requested file is in the list of shared files. The current
version can be downloaded from:

Exploit: Two of us have developed an exploit code for this vulnerability, but we will
not be releasing this to the public.

Conclusion: We have described a vulnerability in one client implementation of
the napster protocol. There may be similar problems in other implementations
of the protocol as we have not done an exhaustive search. The official
Windows client does not seem to be affected. We urge users to upgrade
to the latest version of knapster.